Palladium-nickel alloy plating bath

ABSTRACT

A PALLADIUM-NICKEL ALLOY PLATING BATH IS FORMED OF A SOLUTION OF PALLADIUM SALT AND A NICKEL SALT IN AMMONIA AND A BRIGHTENER IN THE NATURE OF A SULFONATE OR A SULFONAMIDE IS ADDED TO THE BATH IN WHICH A METAL IS PLATED FOR APPROXIMATELY 30 MINUTES AT A PH IN THE RANGE OF 7.5, TEMPERATURE IN THE RANGE OF 30* C., AND CATHODE CURRENT DENSITY IN THE RANGE OF 1 A./DM.2 WITHOUT AGITATION.

United States Patent Int. c1. c231) /32, 5/46 US. Cl. 204-43 5 ClaimsABSTRACT OF THE DISCLOSURE A palladium-nickel alloy plating bath isformed of a solution of palladium salt and a nickel salt in ammonia anda brightener in the nature of a sulfonate or a sulfonamide is added tothe bath in which a metal is plated for approximately 30 minutes at a pHin the range of 7.5, temperature in the range of 30 C., and cathodecurrent density in the range of 1 a./dm. without agitation.

DETAILED DESCRIPTION OF INVENTION The present invention relates to apalladium-nickel alloy plating bath.

In order to eliminate some drawbacks of conventional white metalplatingcomprising silver or nickel, palladiurn plating methods were developer(patent application Sho-39 No. 57,810). We have further succeeded insubstituting a palladium-nickel alloy plating method as differentiatedfrom palladium plating to lower the cost of the deposited layer andwiden its application field. It is an object of the present invention toprovide a palladiumnickel alloy plating bath which has highcorrosion-resistance.

Generally palladium salt and nickel salt are soluble in ammonia solutionto form amino complex salt wherein metal atom is coordinated with NHComplex salt is formed regardless of the nature of acidic radical usedwhich will produce a palladium salt and a nickel salt which eventuallyforms a stable amino complex salt. It was found that when using a bathcomprising amino complex salt of palladium salt and nickel salt thusformed, palladium and nickel codeposit in a form of solid solution alloyand a palladium-nickel alloy can be easily obtained. In addition, thebath for plating was found occasionally to have brightening effect, andsuch efiect is stabilized by adding brighteners such asnaphthalenesulfonate and aromatic sulfonamide. Further examinationrevealed that the palladium content in the codeposited layer can beestablished on any point within the range of 30% and 90% by adjustingthe composition of the bath or plating condition, that the so-platedsurface obtained shows sufiicient brightness and corrosion-resistanceand that accordingly this bath for plating satisfies said object of theinvention.

Referring now to the present invention in more detail, the firstcomposition of the bath for plating, comprises monosalt such aspalladium chloride PdCl and complex salt such as palladous aminochloride Pd(NH Cl are used as supply sources for palladium. As forsupply sources of nickel, nickel sulfate NiSo -7H O', nickel chlorideNiCl '6H O etc. are used. When these palladium or nickel salts are putin aqueous solution of ammonia, the palladium and nickel salts areconverted into the form of amino complex salt. Ammonium salt ofinorganic acid or organic acid such as ammonium sulfate and ammoniumcitrate may be added. 'Ihese additions increase the solubility ofpalladium and nickel, by which stable dissolu- 3,580,820 Patented May25, 1971 tion-.at relatively low pH is achieved. Electroconductivity oftheibath is also improved and at the same time pH is stabilized byvirtue of the product of NH.;+-NH buffer system in the bath. Theconcentration of palladium and nickel in the bath is controlled in sucha manner that as to the quantity of palladium present is S to 30 g./l.and nickel is present in the same quantity i.e. 5 to 30 g./l. The alloyratio of palladium and nickel in the deposited layer depends on theconcentration ratio of palladium and nickel in the bath. As can be seenin the examples below, a combination of 20 g./l. of palladium and 10g./l. of nickel produce alloy deposited layer comprising palladium inthe amount of and alloy deposited layer composed of 60% of palladium isobtained with a combination of 10 g./l. of palladium and 10 g./l. ofnickel. It is not only the concentration ratio of palladium and nickelthat afiects the composition of the alloy deposited layer. Neverthelessother conditions such as pH of the bath, the temperature and cathodecurrent density involve negligible problems because it is easy to keepthese conditions constant during plating operation and except the pH ofthe bath the remaining conditions may be relatively varied withoutadversely affecting the desired results. Therefore desired thecodeposited layer can be obtained if essentially the concentration ofpalladium and nickel in the bath and ratio thereof are controlled withinthe ranges defined.

By adding sulfo compositions such as naphthalenesulfonate or aromaticsulfonamide to said bath, a bright plating can be obtained. Discovery ofthese brighteners gave the bath great practical value. Examples ofnaphthalenesulfonate that can be used are given in the following.

(1) Sodium u-naphthalenesulfonate Sodium p-naphthalenesulfonate S|O3NaSOaNa (2) Sodium 1,S-naphthalenedisulfonate sioaNa SOaNa (3) Sodium1,3,6-naphthalenetrisulfonate s oiNa S OzNa- -S OzNa Thesenaphthalenesulfonates in which aromatic nucleus is combined withsulfonic radical show brightening effect regardless of the numbers ofsulfonic radical and its joined position.

Examples of aromatic sulionamide that can be used are:

(1) Saccharin (2) Paratoluenesulfonamide In these sulfonamides thearomatic nucleus is combined with -SO NH- and its brightening eifect iscaused by the presence of the SO NH.

The composition and internal stress of the deposited layer show nonoticeable change by this bright plating. Satisfactory results can beobtained when said bath is operated at pH 7-10, temperature 15-40 C.,cathode current density 0.5-1.5 ampere/dm using palladium or graphiteanode. During plating concentration of palladium and nickel must beestimated by chemical analysis and always controlled properly. Suppliesof deposition metal is elfectuated by adding said salt directly in thebath. While continuing plating the ammonium salt is graduallyaccumulated in the bath but it has no deleterious effect. The pH isadjusted by adding ammonia water and dilute sulphuric acid. Generally,lowering of pH tends to enlarge the deposition potential of nickel andincrease the nickel content in the deposited layer. It sometimes occursthat palladium content in the deposited layer is not comprised within30% and 90% owing to improper composition of the bath or platingcondition. As the palladium content in the codeposited layer goes farfrom the range of 30 to 90%, solid solution of palladium and nickel isnot formed completely and when applied thick plating plated surfaceloses its brightness and is easy to crack. Other plating conditions arethe same with that of conventional method. There are no restriction asto the kind of the base metals.

The features and principles underlying the invention described above inconnection with specific exemplifications will suggest to those skilledin the art many other modifications thereof.

EXAMPLE 1 A bath containing 20 g. of palladous amine chloride Pd(NH Cl50 cc. of 28% ammonia water and 700 cc. of water was prepared. Thenadded ammonium sulfate of 50 g., nickel sulfate NiSO -7H O of 50 g. andwater sufficient enough to form 1000 cc. of the bath.

A brass test piece was plated in said bath for 30 minutes at pH of 7.5,temperature 30 C., cathode current density 1 a./-dm. without agitation.

Alloy comprising palladium in 60% and nickel in 40% with white brightsurface was obtained from this bath and deposited layer well adhered tothe base.

EXAMPLE 2 Added 10 g. of sodium 1,3,6-naphthalene trisulfonate to thebath of Example 1, and plated for 30 minutes under the same conditionwith Example 1.

10p. of deposited layer with mirror polished surface was obtained.Hv=535 by Vickers hardness tester.

It was exposed to ammonia gas for 24 hours and dipped in artificial seawater for 6 days, after which there found no change at all.

EXAMPLE 3 A bath containing 40 g. of palladous ammine chloride Pd(NH Cl50 cc. of 28% ammonia water and 700 cc.

4 of water was prepared. Then added ammonium sulfate of 50 g., nickelsulfate of 50 g., sodium saccharate NNa-2H2O of 5 g. and water until thebath attains 1000 cc.

A brass test piece was plated in said bath for 30 minutes at pH of 8.8,temperature 30 C., cathode current density 1 a./dm. without agitation.

Alloy comprising palladium in and nickel in 15% with mirror polishedsurface was obtained from this bath and there found no change after 24hours exposure to ammonia gas and 6 days dip in artificial sea water.

What we claim is:

1. A palladium-nickel alloy plating bath having a pH of 7 to 10 composedof ammonia water containing 5 to 30 g./1. of palladium ions, and 5 to 30g./ l. of nickel ions and an alkali metal naphthalenesulfonate in anamount effective for obtaining a bright palladium-nickel alloyelectrodeposited layer in which palladium content is within 30 tothereof.

2. A palladium-nickel alloy plating bath having a pH of 7 to 10 composedof ammonia water containing 5 to 30 g./l. of palladium ions, 5 to 30g./l. of nickel ions and a member of a group consisting of sodiumtit-naphthalenesulfonate, sodium fl-naphthalene-sulfonate, sodium 1,5-naphthalene-disulfonate, and sodium 1,3,6-naphthalenetrisulfonate in anamount effective for obtaining a bright palladium-nickel alloyelectrodeposited layer in which palladium content thereof is within 30to 90%.

3. A palladium-nickel alloy plating bath having a pH of 7 to 10 composedof aqueous ammonia containing in solution a palladium amine complex saltincorporating 5 to 30 g./ 1. of palladium ions, a nickel amine complexsalt incorporating 5 to 30 g./l. of nickel ions and, as brightener, aneffective amount of sodium 1,3,6-naphthalenetrisulfonate whereby abright palladium-nickel alloy electrodeposited layer having a palladiumcontent between 30 and 90% may be obtained.

4. A palladium-nickel alloy plating bath in accordance with claim 3wherein 10 grams of sodium 1,3,6-naphtha- 'lene-trisulfonate is added tothe bath as a brightener for the palladium-nickel alloy.

5. A palladium-nickel alloy plating bath having a pH of 7 to 10 composedof aqueous ammonia containing in solution a salt incorporating 5 to 30g./l. of palladium ions present in the form of palladium-amine chlorideand a salt incorporating 5 to 30 g./l. of nickel ions present in theform of a member of a group selected from an amine nickel sulphate andan amine nickel chloride and a brightener comprising a member of a groupconsisting of sodium a-naphthalene-sulfonate, sodium,B-naphthalene-sulfonate, sodium 1,S-naphthalenedisulfonate, sodium1,3,6- naphthalene-trisulfonate in an amount effective for obtaining apalladium-nickel alloy electrodeposited layer in which the palladiumcontent is within 30 to 90% thereof.

References Cited UNITED STATES PATENTS 1,981,715 11/1934 Atkinson 20447X3,458,409 7/ 1969 Hayaski et a1 20447X FOREIGN PATENTS 958,685 5/ 1964Great Britain 204-47 1,017,950 l/1966 Great Britain 204-47 OTHERREFERENCES Chemical Abstracts, vol. 45, 8317a (1951). R. H. Atkinson etal., Electrometallurgy (Supplement to the Metal Industry), pp. 595-598,June 9, 1933.

GERALD L. KAPLAN, Primary Examiner

